1. Field of the Invention:
This invention relates to a bulldozer blade for an earthmoving vehicle, and more particularly to improvements in the two-way bulldozer mechanism which is movable between a pushing mode and a pulling mode and provides an ample space under push arms above the ground.
2. Description of the Prior Art:
Two different prior art two-way bulldozer blade mechanisms which assume two operational modes are individually shown in FIGS. 1 and 2. For simplicity, only one side is shown and described in the following brief description of each mechanism.
FIG. 1 shows a prior art bulldozer mechanism having upper and lower blades which are hinged together, with the lower blade a pivotally connected to a push arm c by means of a pin d. The upper blade b is connected through the medium of a brace g to the push arm c by means of pins e,f. A pair of levers k are formed on the opposite edges of the lower blade a, while a bifurcated bracket is formed on the top surface of the push arms c, with a hydraulic cylinder j interconnected between the lever k and the aforesaid bracket by means of pins h, i. Thus, the blades give a bend at a hinge point due to the extension and retraction of the cylinder, thereby switching from a pushing mode shown by a solid line to an opposite pulling mode shown by a broken line, and vice versa.
FIG. 2 shows another type bulldozer mechanism presenting a single blade type. The blade a is provided with suitable curvatures on the opposite surfaces thereof, with a connecting lever k secured to the upper portion of the blade a. The tip portion of a push arm c is pivotally connected to the lever k by means of a pin d. A hydraulic cylinder j is interconnected between the lever k and the push arm c by means of pins h and i, which are positioned on the sides of lever k and push arm c, respectively. The blade a switches from a pulling mode shown by solid line to a pushing mode shown by a two point chain line, and vice versa, according to the extension and retraction of a hydraulic cylinder.
Now, the merits and demerits of the aforesaid prior art bulldozer mechanisms will be described hereunder.
The split-type blade assembly as shown in FIG. 1 provides an advantage in that the blade assembly allows the selection of a blade configuration suited for a desired cutting angle, and a trimming or bending angle of mold boards, as required. On the other hand, the aforesaid blade mechanism suffers from a shortcoming in that, since a pivot connection d is positioned in the rear but below the lower blade so as to allow the pivotal movement of the lower blade in the connection d, the attaching position of the push arm is lowered, resulting in interference between materials being removed and the undersurface of the push arm or the undersurface of a cross member interconnecting a pair of push arms, during the trimming operation, whereby the piercing of a blade edge is hindered. To cope with the aforesaid shortcomings, it may be a solution to this problem to provide a push arm, whose attaching portion to the lower blade is bent upwardly so as to give an arch shaped portion. However, such a formation is necessarily subjected to a design limitation and offers many problems arising from the manufacture and rigidity of the push arm.
The bulldozer blade mechanism as shown in FIG. 2 is simple in construction as compared with the blade mechanism of FIG. 1, because of the use of a single blade, and presents an advantage of a wide space under the push arms as well as an excellent piercing capability of the blade, because the attaching positions of the push arms are located in the upper portion of the blade. However, a single blade type mechanism of FIG. 2 fails to provide such desired curvatures as defined by the moldboards of the mechanism of FIG. 1 as well as the cutting angle of the blade edge as provided by the latter. To overcome this shortcoming, the width of the blade may be increased as shown by a one point chain line in FIG. 2, with a resulting increase in weight of the blade itself. In addition, during the unloading operation within a hold of a ship, the outwardly or forwardly projecting portion of the blade interferes with a wall or pole of the hold.
Meanwhile, it is generally accepted principle for a tractor that a bending angle of moldboards should be increased for reducing a load to be imposed on blades as well as for facilitating a bulldozing action of blades in both the forward and rearward directions of movement of a tractor. The blade mechanism of FIG. 2 sacrifices these desired cutting angle and bending angle of moldboards, because of the use of a single blade.